1. Field of the Invention
The present invention relates to a method and apparatus for measuring a displacement in a longitudinal direction of a track recorded on a magnetic tape.
2. Description of the Prior Art
In recording a video signal on a magnetic tape, normally a video image of 1 field constituted by a plurality of scanning lines is recorded as a single track. Accordingly, signals of the plurality of scanning lines are recorded in a longitudinal direction of the track, and horizontal scanning signals are recorded at constant intervals at the boundaries thereof. However, when the signal recording interval in the longitudinal direction of a track fluctuates according to the variations of the magnetic tape running speed and the like, collapse may occur in the recorded interval of the horizontal scanning signal. When the horizontal scanning signals are recorded at varying intervals, distortion occurs on the video image. This is a condition called jitter. Thus, fluctuation of the recording position of the signal in the longitudinal direction of a track is a significant matter which causes a deterioration of the video image.
Conventionally, evaluation of jitter has been performed by reading out the horizontal scanning signal recorded on the magnetic tape or a signal for measurement of time fluctuations recorded on the magnetic tape by a rotating head and measuring the fluctuation of said signals (e.g., Japanese Patent Publication No. 61-18804/1986).
However, according to the conventional method as described above, there has been a problem that, as the jitter is detected under the condition where the factor based on the inequality of intervals of the horizontal scanning signals recorded on the magnetic tape and the factor attributed to the structural system of the recording apparatus including the rotating head are mixed, such a state becomes an obstacle to the case of clarifying the cause for the jitter based on the individual factors.